Carotenoids are natural pigments that are useful as feed additives, food additives, pharmaceutical agents, and the like. Examples of carotenoids include zeaxanthin, β-carotene, β-cryptoxanthin, astaxanthin, canthaxanthin, lycopene, phoenicoxanthin, adonixanthin, echinenone, asteroidenone, and 3-hydroxyechinenone.
Among carotenoids, zeaxanthin is a natural yellow pigment contained in various plants such as corn, and known to be applied for improving the color tone of egg yolk, meat, or skin of a poultry such as a chicken by being added to feed and be used as a coloring agent for foods. Zeaxanthin also has been reported to have a potent antioxidant function (Non-Patent Document 1) and an anti-tumor effect (Non-Patent Document 2). Further, zeaxanthin is known to be, together with lutein, present in the retina and crystalline lens and involved in the maintenance of eye health (Non-Patent Document 3). Due to these physiological effects, zeaxanthin is useful as a material for health foods, cosmetics, or pharmaceuticals.
β-Cryptoxanthin is contained in citrus fruits, known to have an anti-tumor effect (Non-Patent Document 2), and reported to have an effect of preventing osteoporosis (Non-Patent Document 4). β-Cryptoxanthin is applied for a health food material or a feed additive.
β-Carotene has provitamin A function and antioxidant function and is widely used as a feed additive, food additive, natural coloring agent, or the like.
When zeaxanthin, β-cryptoxanthin, or β-carotene is added to feed for a poultry such as a chicken and the feed is given to the poultry, it accumulates in egg yolk. Since carotenoids have the above physiological effects, eggs in which these carotenoids have accumulated in egg yolk are useful as functional eggs.
Known examples of methods for producing zeaxanthin include chemical synthesis using, as a raw material, an optically active hydroxyketone obtained by asymmetric reduction of oxoisophorone (Non-Patent Document 5) and extraction from corn seeds. Extraction of zeaxanthin from marigold is also known (Patent Document 1); however, a marigold-derived carotenoids mainly contain lutein and have a reduced content of zeaxanthin.
Known examples of microorganisms that produce zeaxanthin include Spirulina algae (Patent Document 2), Nannochloris spp. microalgae (Patent Document 3), Flexibacter spp. bacteria (Patent Document 4), Alteromonas spp. bacteria (Patent Document 5), Flavobacterium spp. bacteria, and Agrobacterium aurantiacum (Non-Patent Document 6). In addition, among bacteria belonging to the genus Paracoccus known as carotenoid-producing bacteria, the following examples are known as strains that produce zeaxanthin: Paracoccus zeaxanthinifaciens strain ATCC 21588 (Non-Patent Document 7), a mutant strain of Paracoccus carotinifaciens strain E-396 (Patent Document 6), a mutant strain of Paracoccus bacterial strain A-581-1 (Patent Document 6), and a mutant strain of Paracoccus bacterial strain (Patent Document 7).
However, the above method for producing zeaxanthin by chemical synthesis have problems in terms of safety because of use of organic solvents and also in terms of the directional trend of recent years toward a natural product. In addition, zeaxanthin production via culturing algae is not practical because of low productivity. Further, extraction of zeaxanthin from a plant has the disadvantages of requiring too much cost because of low zeaxanthin content thereof and difficulty of stable supply due to weather dependency.
Meanwhile, bacteria belonging to the genus Paracoccus are advantageous in that proliferation rates thereof are fast, carotenoid productivity thereof is high, and carotenoids can readily be extracted therefrom, etc. However, large amounts of gluconic acid are produced in a culture liquid of such a bacterium, resulting in waste of a carbon source. In addition, accumulated gluconic acid suppresses production of zeaxanthin. Thus, it was impossible to accumulate and produce zeaxanthin at a sufficient concentration in terms of production cost efficiency. Thus, there is need for an inexpensive method for producing zeaxanthin with high safety, by which zeaxanthin can be stably supplied.